1. Field of the Invention
The present invention relates to a poyurethane elastomer. More particularly, the present invention relates to a polyurethane elastomer useful for a sealing material in electrical appliances, and a terminal bundling material for medical and industrial hollow-fibers.
2. Related Background Art
Heretofore, polyurethane type bundling materials used for sealing materials in electrical appliances and for hollow-fibers in medical liquid-separating apparatuses have been made from an aromatic polyisocyanate such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), etc. as the isocyanate compound, and a castor-oil-type polyol, a polyether-type polyol, polyester-type polyol or an amine-type polyol as the polyol component. In the case of use for bundling hollow-fibers in medical liquid separation apparatuses, however, the elastomer is required to contain far less substance which may be eluted from the sealing portion. For the improvement thereof, Japanese Patent Laid-open Application Sho. 60-58156 discloses the use of a prepolymer prepared by reaction of hexamethylene diisocyanate (HMDI) with a polyol as a fraction of the polyisocyanate component. However, the prepolymers, which have been prepared by reaction of HMDI with a polyol such as 1,4-butanediol, castor oil, etc., generally contain a large amount of unreacted HMDI. Thus, the use of such prepolymer as the starting material for the bundling material is undesirable from the stand point of safety and hygiene of the workers, as well as insufficient in the decrease of the eluted matter from the cured polyurethane. Accordingly, further decrease of the unreacted HMDI is required.
Moreover, HMDI has the disadvantage of significantly low reactivity, causing slow curing after potting, with low productivity, as compared with aromatic diisocyanate, e.g., TDI and MDI.
A method for promoting the reaction of such polyisocyanate and a polyol is disclosed by Japanese Patent Laid-open Application Sho. 58-93716, in which a metal type catalyst, etc. are employed for shortening the curing time. However, the employed heavy metal such as Sn, Pb, Zn, Cd, etc., if eluted out, exerts harmful effects to a living body or deteriorates electrical properties, so that the use of such metal-type catalyst is not desirable for medical materials nor electrical materials.
Starting materials for polyurethane elastomers are required to have a viscosity suitable for potting to cause neither deterioration nor denaturation of quality of the cured products, even after storage, to exhibit stable performances.